Minecraft 1.7.6 or newer (UUID)
On Minecraft 1.7.6 and above, Mojang uses a new UUID format. Use a UUID lookup tool, like http://minecraft-techworld.com/uuid-lookup-tool to determine the UUID of the player you wish to reset.
- Make sure that the player you wish to reset is logged out of the server.
- Use FileZilla to connect to the server FTP.
- On the remote site, open the game folder.
- Open the world folder. It is usually world, unless you have changed it.
- Open playerdata.
- Simple: Delete, or download/rename and then delete, uuid.dat. Replace uuid with the UUID that you looked up.
- Advanced: Instead of deleting uuid.dat, download it to a location on your computer such as your desktop where you can easily find it.
- From NBTExplorer, press the “Open NBT Data Source” button that looks like a folder.
- Navigate to where you saved the uuid.dat file, select it, and press open.
- Scroll down untill you find the tag labeled “Pos” with 3 entries and press the “+” symbol next to it. These are the data tags that store where a player is in game.
- Double click on the tags one at a time and change their values. The tags aren’t labelled, but they are X, Y, Z in that order. Y is height. Be careful what you set these numbers to as you can cause a player to spawn in the ground. I suggest setting their value to your world’s spawn or a known safe coordinate location.
- Upload the uuid.dat back to your server in the same place you got it. Overwrite or delete the original one. Make sure that the player in question is not online at the time or it won’t work.